The EOSC-Life project aims to integrate data resources and data processing workflows developed by and in collaboration with the Life Science Research Infrastructures (LS RIs) in the European Open Science Cloud (EOSC). This Work Package, WP3, has the objective to identify scientific user projects that will drive this integration and that will allow the scientific community to shape the building of the EOSC for the life sciences by expressing their needs, and by feeding in their requirements. With this document, WP3 presents the guidelines on the preparation, organization and framework of Open Calls for User Projects that will be the main tool for the identification of suitable projects. The Open Calls are designed to contribute to achieving the overarching goal of WP3: to enable EOSC-empowered ground-breaking research, and to generate new knowledge by linking the life science communities to a variety of data resources and a platform of various data analysis tools. By identifying and selecting suitable user projects, WP3 will take a pragmatic approach for populating as well as developing solutions and testing of the EOSC for life sciences. Reusing FAIR data resources and having workflows run in the cloud is becoming increasingly important for researchers, however, building and spreading of cloud technology related skills is still needed for many researchers. WP3 will address those scientists via Open Calls by offering applicants training and consultation with experts across the EOSC-Life consortium. By providing funding, WP3 will also empower scientific groups that have built the capacity and skill sets to run their projects mostly independently or in collaboration. Importantly, selected projects are expected to have a lasting impact and to leave behind some legacy, so that future projects can benefit from their work and re-use their data, tools or workflows. Projects should present novelty in terms of the interplay between RIs and the EOSC, and address important challenges and needs of the life science community.